Thermoplastic materials are widely used as a material for articles of manufacture. For instance, it is known in the art to use thermoplastic polyvinyl chloride (PVC) to mold articles of furniture such as chair frames and other furniture articles. The PVC resin is often provided with an integral wood grain finish to simulate the appearance of real wood. While thermoplastic polymer sheets and profiles offer high impact resistance, the wear resistance and abrasion resistance is low.
It is difficult to obtain extruded sheets such as PVC having therein a good wood grain appearance over a wide sheet width. A wood grain effect is achieved in an extruded sheet by forcing a cylinder of molten polymer at high pressure from an extruder barrel through a die which directs the molten thermoplastic material into a flattened, rectangular shape. To achieve a wood grain effect, plastic pellets are added which only partially melt as they go through the extruder. The resin pellets which provide the wood grain appearance are selected from materials having higher melting points than the base polymer. In a typical extruder/die combination for extruding flat sheets, the center of the die has a lower resistance to molten plastic flow than the edges of the die. As a result, the molten plastic flows more easily through the middle of the die as opposed to the edges of the die. Because of lower shear along the center of the die, the pigmented pellets preferentially flow through the die center. As a consequence, the molten sheets typically exhibit a more pronounced grain pattern in the middle of the sheet. The intensity of the grain degrades towards the edges of the sheet, the effect becoming more noticeable as the width of the extruded sheet increases. As a result, there remains a need within the art for developing improved extrusion techniques which provides for an enhanced grain appearance across the entire width of an extruded sheet.
It is also known to apply decorative films, papers, and surface polymer layers to the laminated structure to improve the appearance of the product. However, such overlayments are often thin and, hence, prone to damage and not easily repaired.
U.S. Pat. No. 6,106,654 provides a thermoset laminate in which a paper web impregnated with melamine-formaldehyde resin is applied as a surface layer to the laminate. The sheet is coated with the impregnated paper, one side of the paper containing aluminum oxide particles.
U.S. Pat. No. 5,763,048 discloses a PVC substrate having a protective layer of a cured resin having polycarbonate particles mixed with the resin. The resin is cured by applying ionizing radiation to the PVC substrate.
U.S. Pat. No. 4,921,669 discloses scratch resistant coating suitable for use with a PVC substrate in which a separate coating of a monomer mixture is applied to the PVC surface by polymerization. The monomer has a high cross-linking density and provides good scratch resistance.
While there are a variety of scratch resistant coatings and resins known within the art, there remains room for improvement and variation within the art.